Roofing paper or mat is commonly provided with guide lines which are useful to workmen in applying built-up roofing. The lines are typically parallel to each other and spaced apart a predetermined distance so that when used as a guide for the edge of the next course of mat, overlapping layers of the mat can be readily applied according to the type of coverage desired. For example, when mat is applied with its upper edge aligned with a particular guide line double coverage of the roof would result; when aligned with another particular line, triple coverage would result, and so on.
Although various types of indicia have been used to form the guide lines the most desirable is a marking formed of paint. A paint line can readily be seen by the roofer and allows guide lines of different colors to be employed, with the colors being correlated to the various roof coverages likely to be used.
Paint guide lines are commonly formed by the so-called "marking wheel" method. In this method a number of discs are mounted on a common shaft adjacent the moving web of mat in a roofing machine. The shaft extends in a transverse direction to the movement of the web and is located downstream from the asphalt application station. The bottom portions of the discs move through a reservoir of paint, picking up a sufficient amount to be deposited onto the adjacent surface of asphalt impregnated mat. Although this process results in colored guide lines useful to the roofer in the application of the roofing product, the method of applying the paint tends to cause problems.
The very high speeds at which the mat travels in a modern roofing machine leaves little tolerance for variations in the amount of paint applied. If too little is applied the guide line may be too faint to be easily discerned in the field. If too much is applied, the paint tends to build up on the various rolls of the roofing machine located downstream from the paint application station. This eventually requires premature shutdown of the machine for cleaning, resulting in excessive downtime. In addition, too much paint tends to cause cracking of the roofing paper, apparently caused by the inability of the paper to take up stresses at the locations of paint during its high speed run through the roofing machine. To the extent that excessive amounts of paint resemble imperfactions in the mat, too much paint also tends to make the web susceptible to sailing, or moving in a transverse direction from its intended path of movement.
It would be highly desirable to be able to mark roofing paper with painted guide lines in order to derive the beneficial aspects of such markings, but without the detrimental features associated with the normal method of paint application.